From mboxrd@z Thu Jan 1 00:00:00 1970 From: ron@ronnatalie.com (Ronald Natalie) Date: Tue, 6 Jan 2015 16:57:14 -0500 Subject: [TUHS] pdp11 UNIX memory allocation. In-Reply-To: <1420576433.410248.210385277.513EF8EC@webmail.messagingengine.com> References: <54AC4394.3050302@update.uu.se> <1420576433.410248.210385277.513EF8EC@webmail.messagingengine.com> Message-ID: <5E62DDAA-0055-46FB-8077-92DB856DEEE0@ronnatalie.com> > On Jan 6, 2015, at 3:33 PM, random832 at fastmail.us wrote: > > Was it possible to read/write to the instruction space, or execute the > data space? In split I/D mode (411) magic number. It is imposible to execute in D space or use regular data access instructions to access i-space. The addresses are in completely different spaces (i.e, 0 in data is mapped to different memory than 0 in instruction space). Some access at the kernel level can be done with MFPI and MPFD instructions. In write protected, non-split more (410 magic), you could read the I space and you could jump in to D space. You were prohibited to write the i space. In non protected mode (407 magic) everything was fair game.